The present invention concerns capacitors, particularly wet-electrolytic capacitors used in implantable medical devices, such as implantable defibrillators, cardioverters, and pacemakers.
The present invention concerns implantable heart monitors, such as defibrillators and cardioverters, particularly structures and methods for capacitors in such devices.
Since the early 1980s, thousands of patients prone to irregular and sometimes life-threatening heart rhythms have had miniature heart monitors, particularly defibrillators and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The typical defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the walls of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.
The capacitor is often times a cylindrical aluminum wet electrolytic capacitor. This type capacitor usually includes stacked strips of aluminum foil and paper rolled, or wound, to form a cylindrical structure which is housed in a round tubular aluminum can. The can has an integral aluminum bottom end and an open top end sealed with a non-conductive flat circular lid, known as a header. Two terminals extend from the header, each connected to one of the rolled aluminum foils.
One problem the inventors recognized with these cylindrical capacitors is the overall height of the capacitor, measured from the bottom of the tubular aluminum can to the top of the terminals extending from the header. In particular, the terminals are rigid metal structures that generally require clearance space to avoid contacting other components within the housing of the implantable devices. Providing this clearance space ultimately increases the size of implantable devices beyond that otherwise necessary. Another related problem is that the diameter of the header has a practical minimum of about twelve millimeters and thus restricts how small capacitors and thus implantable devices can be made. Accordingly, the inventors identified a need to develop space-efficient techniques and structures for providing terminals on electrolytic capacitors.
To address this and other needs, the inventors devised wet electrolytic capacitors with unique connection structures. One exemplary capacitor includes two conductive endcaps at opposite ends of its capacitive element, instead of two upright terminals at one end, thereby allowing reduction in the height or volume of the capacitor and/or increases in the dimensions of other components, such as aluminum foils. Another exemplary capacitor includes two feedthrough assemblies at opposite ends of the wound capacitive element to also facilitate reduction in the height or volume of the capacitor or increasing its energy-storage density.
Other aspects of the invention include an implantable heart monitor, such as a pacemaker, defibrillator, congestive-heart-failure (CHF) device, or cardioverter defibrillator, that incorporates one or more capacitors with the unique connection structures.